The present invention relates to a thermoplastic composite member consisting essentially of a thermoplastic matrix resin and reinforcing fibers and having improved toughness, a thermoplastic composite fabric for producing such a thermoplastic composite member, an assembly of a bagging film and a seal member for the high-temperature forming of a thermoplastic composite member, a method of producing a thermoplastic composite member, a preform composed of a thermoplastic composite member and a method of producing such a preform without suffering from wrinkles, a formed article constituted by two or more thermoplastic composite members free from insufficient bonding between thermoplastic composite members, and a method of producing such a formed article.
Various composite members consisting essentially of various matrix resins and reinforcing fibers such as carbon fibers have been used as alternatives of metal members for many applications. Since composite members having matrix resins made of thermoplastic resins can easily be molded or formed, they are used for wide applications such as home electric appliances, machine parts, automobile parts, structural members, etc. Since thermoplastic composite members are excellent in mechanical strength with light weight, they may be used in many fields in which conventional resins are not satisfactory from the aspect of mechanical strength. Particularly, since polyether ether ketone (hereinafter referred to as "PEEK"), one of thermoplastic resins, has good mechanical strength, high elongation, etc. and can withstand large damage, it has been investigated to use this PEEK as a matrix resin for fiber-reinforced composite members in various machine parts such as automobile parts, structural members, etc.
A typical composite fabric consisting essentially of a matrix resin made of the PEEK resin and reinforcing fibers (reinforcing fibers/PEEK composite) is a sheet-like member obtained by weaving reinforcing fibers such as carbon fibers and fibers made of PEEK. The production of a formed article from these sheet-like fabrics is usually conducted by laminating a plurality of sheet-like fabrics and heating the resulting laminate under pressure, thereby melting the PEEK into an integral form.
Although a composite member consisting essentially of a PEEK matrix resin and reinforcing fibers shows good mechanical strength, it has been found to be somewhat poor in impact resistance, etc. To obviate this problem, it is necessary to improve the toughness of the composite member. For this purpose, it is preferable to use a high-molecular weight PEEK as a matrix resin. However, since the high-molecular weight PEEK has a large melt viscosity, the reinforcing fibers cannot be well impregnated with melted high-molecular weight PEEK in the composite fabrics. Therefore, in conventional composite fabrics of reinforcing fibers/PEEK fibers, low-molecular weight PEEK fibers are used to make sure that the reinforcing fibers are well impregnated with the PEEK.
When the low-molecular weight PEEK is used, the resulting composite member, particularly a matrix portion thereof, does not show highly improved toughness. Accordingly, the toughness of the conventional composite members formed by simply laminating composite fabrics consisting essentially of reinforcing fibers and PEEK fibers is not satisfactory for applications such as automobile parts, structural members, etc.
In the production of thermoplastic composite members from thermoplastic composite fabrics, uniform pressure should be applied to the thermoplastic composite fabrics which are kept in desired shapes while being in good contact with each other or with different members. To achieve this object, a laminate of the thermoplastic composite fabrics is placed on a base plate made of aluminum, etc., laying a heat-resistant seal member around the base plate, covering the laminate on the base plate with a heat-resistant film such as a polyimide film, a nylon film, etc. (bagging film) for conducting the high-temperature forming of the thermoplastic composite fabrics at 250.degree. C. or higher, bonding the bagging film to the seal member, and then heating the laminate in the bagging film to produce an integral thermoplastic composite member.
One example of such a bagging film is shown in FIG. 6. Placed on a base plate 21 made of aluminum, etc. is a laminate 22 of thermoplastic composite fabrics encircled by a frame 23. The laminate 22 is properly covered with a peel ply 24, a parting film 25 having apertures, a bleeder 26, a parting film 27, a press sheet 28 and a breather 29, if necessary. Placed outside the frame 23 is a heat-resistant seal member 30 for bonding the heat-resistant bagging film 31 to the base plate 21.
After bagging, the laminate 22 is heated under pressure to form an article having a desired shape. At this time, by evacuating the air from the heat-resistant bagging film 31 by a vacuum pump, it is possible to prevent the formed article from being deformed or from being hardened at different speeds from place to place, while removing small bubbles from the composite member.
However, since the heat-resistant bagging film 31 is rigid (poor in softness), and since the heat-resistant seal member 30 shows poor adhesion property at room temperature, the bonding operation of the seal member 30 to the bagging film 31 cannot be conducted efficiently. In addition, when the bagging film 31 is evacuated by a vacuum pump, leak is likely to take place particularly between the bagging film 31 and the seal member 30.
Apart from the above problems, it is generally difficult to bend a thermoplastic composite member composed of a plurality of thermoplastic composite fabrics without wrinkles in the process of forming, because a radius of curvature is different between fabrics near inside and those near outside. Accordingly, when bent articles are produced, sheet-like, thermoplastic composite fabrics to be laid outside should have larger lengths than those laid inside. According to this principle, the lengths of thermoplastic composite fabrics should increase gradually from inside to outside. The thermoplastic composite fabrics thus laminated on a mold or a jig are then heated under pressure to provide a bent article.
However, it is a laborious job to change the lengths of sheet-like, thermoplastic composite fabrics properly depending on the degree of bending.
In addition to the above, in a case where such a thermoplastic composite member is used as a structural member, for instance, an H-shaped structural member as shown in FIG. 14, two flat thermoplastic composite members 61, 62 and one thermoplastic composite member 63 having both end portions 63a, 63a, 63b, 63b opened substantially perpendicularly are first prepared, and the opened end portions 63a, 63a, 63b, 63b of the thermoplastic composite member 63 are abutted and pressed onto the flat surfaces of the thermoplastic composite members 61, 62 while heating. However, for the same reason as mentioned above, the outside portions of the thermoplastic composite member 63 suffer from wrinkles after bending. Further, since the solidified thermoplastic composite members 61, 62 and the solidified thermoplastic composite member 63 are abutted, it is difficult to bend the thermoplastic composite member 63 completely perpendicularly, resulting in a bonded thermoplastic composite member with a slight gap in a center portion "g." In the process of heating and pressing, the gap portion "g" serves as a void or a resin-rich portion, whereby the resulting formed article shows insufficient strength in the gap portion "g."
It is possible to laminate a plurality of thermoplastic composite fabrics having gradually increasing lengths from inside to outside to avoid wrinkles after bending, but even with such thermoplastic composite fabrics, the gap "g" cannot be removed.